1. Field of the Invention
The preset invention relates to a scanning circuit which is suitable for scanning large-scale liquid crystal displays.
2. Background Art
Conventionally, there is known a technology in which a liquid crystal display is integrated together with its driving circuit on a glass substrate. Accordingly to this technology, electrodes for the pixels of the displays and the driving circuits are mounted on the same substrate. Because of this, the number of terminals and the number of required external ICs are sharply reduced. Furthermore, lowered reliability, which is caused by efficiency limits of bonding processes for large surface areas of the circuits and the high-densities of the circuits, can be resolved.
In the driving circuit, a scanning circuit consisting of shift-registers and buffers is provided. For example, in an active-matrix type liquid crystal display, the scanning circuit is used as one of the important constituents such as a vertical driving circuit or a block pulse scanning circuit.
In FIG. 6, a (2N-1)th bit part and a 2Nth bit part of a conventional scanning circuit is shown (where N equals a natural number).
Each shift-register 601 delays an input signal thereto for a prespecified clock cycle which is defined by clock signals .phi.1 and .phi.1, and then generates the delayed signal to a shift register in the next stage. Signals respectively generated by the registers 601 are generated as a scanning pulse signal via corresponding output buffers 107. FIG. 7 is a timing chart showing an operation of the conventional scanning circuit shown in FIG. 6. As shown in FIG. 7, the scanning pulse signals generated from the (2N-1)th bit part and the 2Nth bit part are respectively synchronizing with corresponding output signals A and B.
Recently, the surface areas of liquid crystal displays have been enlarged; so that it have been difficult to manufacture the associated circuits of the displays without any defects. In particular, if only one defective register appears in a scanning circuit which contains serially connected shift registers as shown in FIG. 6, the scanning circuit will not transmit the scanning signal.
Accordingly, the percentage of defective scanning circuits and therefore percentage of defects of entire liquid crystal displays have been increased.